1. Overview of Cellular Respiration, Photosynthesis and Redox Reactions
Lecture 6
Fall 2008

2. Working Cells All organisms need ATP to do cellular work1
All organisms need ATP to do cellular work
Cells get ATP from converting carbon compounds (chemical energy) through cellular respiration
Cellular Respiration:
The conversion of chemical energy of carbon compounds into another form of chemical energy, ATP
Where does an organism get the chemical energy (carbon compounds) used in cellular respiration?

3. Food Chains Producers Autotrophs (self-feeders)2
Producers
Autotrophs (self-feeders)
Use photosynthesis or chemosynthesis to make organic food molecules
Plants, algae (phytoplankton), cyanobacteria
Basis for all other ecosystem growth
Primary productivity
Productivity: amount of biomass produced in a given area during a given period of time
Biomass: dry weight of all organic matter in an organism
Fig

4. Cellular Respiration & Photosynthesis3
Photosynthesis
The process by which light energy from the sun is converted into chemical energy
Chemical energy in the form of organic compounds

5. Food Chains Consumers Heterotrophs (other-feeders)4
Food Chains
Consumers
Heterotrophs (other-feeders)
Obtains organic food molecules by eating other organisms or substances derived from other organisms
Primary = herbivores
eat producers
Secondary = carnivores
eat herbivores
Tertiary = top carnivores
eat other carnivores
Fig

6. 5
Metabolic Diversity
Phototrophs: Organisms that obtain energy from light
Chemotrophs: Organisms that obtain energy from inorganic or organic compounds in their environment
Autotrophs: Organisms that need only inorganic molecules (CO2 or CH4 ) as a carbon source
Heterotrophs: Organisms that require at least one organic nutrient (e.g., glucose) as a carbon source

7. Cellular Respiration & Photosynthesis6
Cellular Respiration & Photosynthesis
Cellular respiration requires carbon compounds & oxygen
Carbon compounds & oxygen produced by photosynthesis
See Fig. 9.2

8. Cellular Respiration Catabolic pathway Aerobic respiration7
Catabolic pathway
Aerobic respiration
Consumes oxygen
Anaerobic respiration
Use other molecules (not oxygen)
Catabolic pathway
Breaks down a complex molecule into simpler compounds
Creates energy
harvesting of chemical energy from organic fuel molecules

9. Cellular Respiration 8
Cellular respiration is not the same as gas exchange (respiration)
Gas exchange is the exchange of O2 and CO2 between an organism and its environment
Cellular respiration is not the same as breathing
“Breathing” refers specifically to process in lungs

10. Cellular Respiration Glucose molecule held together by covalent bonds9
Cellular Respiration
Glucose molecule held together by covalent bonds
Covalent bonds share electrons
Cellular respiration changes which atoms are bonded together
ΔG = kcal/mol

11. Redox Reactions Redox reactions =oxidation-reduction reactions10
Redox reactions =oxidation-reduction reactions
Chemical reactions that transfer electrons from one substance to another
Oxidation
The loss of electrons
Reduction
The addition of electrons
Reduction reduces the positive charge of an atom
Reducing agent = electron donor
Oxidizing agent = electron acceptor

12. Redox Reactions Energy needed to pull electrons away from an atom11
Redox Reactions
Energy needed to pull electrons away from an atom
Requires more energy the more electronegative the atom
Electronegativity : The tendency of an atom to attract electrons towards itself
Electrons lose potential energy as they move from less electronegative to more electronegative atom
Releases energy

13. Redox Reactions in Cellular Respiration12
When glucose is broken down, hydrogen and its electrons change partners
Electrons lose potential energy along the way and energy is released
Oxidation
Glucose oxidized
Reducing agent - Loses electrons
Reduction
Oxygen reduced
Oxidizing agent - Gains electrons

14. Electron Acceptors High electronegativity13
High electronegativity
Electrons move from molecule to molecule by being “passed” to a stronger electron acceptor
Electron Acceptors
NAD+ (nicotinamide adenine dinucleotide)
Positively charged electron acceptor
NAD+ is reduced to NADH
NADP+ (nicotinamide adenine dinucleotide phosphate)
Reduced to NADPH
FAD (flavin adenine dinucleotide)
FAD is reduced to FADH2
Oxygen
Can accept (“pull”) electrons from both NADH & FADH2

15. Electron Transport Chain14
Why can’t the electrons be transferred from glucose to oxygen in one step?
Too explosive
Energy released as heat and light energy
Not readily usable to do work
Breaking it down into steps allows the energy to be used to perform work
= Electron Transport Chain
Fig. 9.5

16. Electron Transport Chain15
Electron Transport Chain
Used to slow the fall of electrons from glucose to oxygen
“chain” of protein complexes (and other molecules)
Electrons pass from molecule to molecule in a series of redox reactions
At each step, energy is released
Used in the synthesis of ATP
Fig. 9.5

17. Electron Transport Chain16
At bottom of chain, the electron “drops” to oxygen
Oxygen also picks up hydrogen and forms H20
Oxygen is driving the “fall” by attracting the electrons
Fig. 9.5
Fig. 6.6